The present invention relates to vane oscillators and, in particular, it concerns a liquid-sealed vane oscillator and systems of such oscillators.
Attempt shave been made to develop a liquid-sealed vane oscillator in which a liquid film provides a seal around a vane element oscillating within a cavity. Reference is made to U.S. Pat. No. 5,115,157 to the present inventor which describes such a device.
The device described in the aforementioned patent employs a vane oscillating in an annular cavity around a central axis. The cavity is divided into two chambers so that oscillations of the vane generate alternating out-of-phase variations of pressure within the chambers. Narrow gaps between the vane and the walls of the cavity are sealed by a sealing liquid which provides a dynamic seal. The sealing liquid is also intended to serve as a heat-exchange liquid in direct contact with the gas within the chambers to make the device capable of near-isothermal operation.
The device described has been found unsuitable for relatively high pressure differential applications. Specifically, when pressure in one chamber increases, the resulting pressure differential tends to force the sealing liquid between the vane and the cavity wall into the second working chamber, thereby reducing the effectiveness of the seal. As a further consequence, the quantities of liquid normally present in the chambers during operation are very high, making the design ineffective due to mechanical losses from the liquid impacting against the vane and from two-phase flow friction through the discharge valves.
An additional shortcoming of the device of the aforementioned patent relates to the drive mechanism. The patent suggests the use of a 4-bar linkage of the Grashof chain type for "effecting a controlled amplitude harmonic vane motion". In practice, however, this type of transmission is limited to use with one vane oscillator or cylinder and becomes cumbersome when applied to two or more cylinders. It is also difficult to balance inertial forces in the 4-bar linkage to achieve reduced vibration even with a single cylinder.
In a further example of a prior art liquid-sealed compressor, a Swiss company "Burckhardt" of Basel, Switzerland, at one time offered for sale a reciprocating oxygen compressor equipped with automatic force-feed lubrication acting on the principle of an automobile carburetor. The lubricating water was drawn into the inlet flow of oxygen by the suction effect of a venturi section of pipe. The water was then removed from the outlet flow by a separator and fed back to the supply system by the pressure difference between the compressor inlet and outlet. The water introduced into the compressor not only acted as a sealing liquid and lubricant, but also provided some degree of internal, evaporative cooling.
The evaporative cooling in the Burckhardt design only provided partial removal of the heat of compression and was incapable of providing heat exchange for expansion. True isothermal compression by the method of Direct Contact Heat Exchange (DCHX) where significant heat is transferred to the cooling liquid from the gas would require much more liquid throughput than is possible with the Burckhardt carburetor.
There is therefore a need for a liquid-sealed vane oscillator which is capable of operating with high pressure differentials, and in which the sealing liquid is effective as a heat-exchange medium for producing near-isothermal operation. It would also be advantageous to provide a liquid-sealed vane oscillator system in which a number of oscillators are engaged synchronously with low levels of vibration.